Bridgeless pfc power converter with high efficiency

ABSTRACT

A bridgeless PFC boost converter has two auxiliary transistor switches coupled to an input AC voltage source and two boost inductors coupled to opposing ends of the input AC voltage source. A first boost inductor is coupled to a junction node of a first rectifying diode and a first transistor switch coupled in series. A second boost inductors is coupled to a junction node of a second rectifying diode and a second transistor switch coupled in series. The rectifying diodes are commonly coupled to an output capacitor, and the transistor switches are commonly coupled to a second node of the output capacitor. A first auxiliary transistor switch is commonly coupled with the first boost inductor and to a first node of the input AC voltage source. A second auxiliary transistor switch is commonly coupled with the second boost inductor and to a second node of the input AC voltage source.

RELATED APPLICATIONS

This Patent Application claims priority under 35 U.S.C. 119 (e) of the co-pending U.S. Provisional Application, Ser. No. 61/829,119, filed May 30, 2013, and entitled “Bridgeless PFC Power Converter with High Efficiency”. This application incorporates U.S. Provisional Application, Ser. No. 61/829,119 in its entirety by reference.

FIELD OF THE INVENTION

The present invention is generally directed to the power converters. More specifically, the present invention is directed to a bridgeless power factor correction (PFC) power converter with high efficiency.

BACKGROUND OF THE INVENTION

Power conversion refers to the conversion of one form of electrical power to another desired form and voltage, for example converting 115 or 230 volt alternating current (AC) supplied by a utility company to a regulated lower voltage direct current (DC) for electronic devices, referred to as AC-to-DC power conversion.

A switched-mode power supply, switching-mode power supply or SMPS, is a power supply that incorporates a switching regulator. While a linear regulator uses a transistor biased in its active region to specify an output voltage, an SMPS actively switches a transistor between full saturation and full cutoff at a high rate. The resulting rectangular waveform is then passed through a low-pass filter, typically an inductor and capacitor (LC) circuit, to achieve an approximated output voltage. The switch mode power supply uses the high frequency switch, the transistor, with varying duty cycle to maintain the output voltage. The output voltage variations caused by the switching are filtered out by the LC filter.

An SMPS can provide a step-up, step-down or inverted output voltage function. An SMPS converts an input voltage level to another level by storing the input energy temporarily and then releasing the energy to the output at a different voltage. The storage may be in either electromagnetic components, such as inductors and/or transformers, or electrostatic components, such as capacitors.

Advantages of the SMPS over the linear power supply include smaller size, better power efficiency, and lower heat generation. Disadvantages include the fact that SMPSs are generally more complex than linear power supplies, generate high-frequency electrical noise that may need to be carefully suppressed, and have a characteristic ripple voltage at the switching frequency.

High-frequency ripple results when passing current through the transistor switches and then filtering the current with passive components. The frequency components of the ripple are dependent on both the switching frequency and the switching speeds of the semiconductor switches. The high-frequency ripple generates unwanted electromagnetic interference (EMI) and must be removed to a high degree for the converter to pass standard EMI requirements.

Conventional power converters pass EMI requirements by reducing the input and output ripple. Reduction is accomplished by the following methods: large filters, reduction of switching frequency, and/or reduction of switching speeds. Such techniques are commonly practiced in nearly all conventional power converters. However, use of each of these techniques comes with specific drawbacks. Use of large filters adds space and cost. Reduction of switching frequency increases the size of passive components and cost. Reduction of switching speeds reduces efficiency.

The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power, and is a number between 0 and 1. Real power is the capacity of the circuit for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power can be greater than the real power. Low-power-factor loads increase losses in a power distribution system and result in increased energy costs. Power factor correction (PFC) is a technique of counteracting the undesirable effects of electric loads that create a power factor that is less than 1. Power factor correction attempts to adjust the power factor to unity (1.00).

High power applications, and some low power applications, require the converter to draw current from the AC line with a high power factor. Boost converters are commonly used to produce the high power factor input. A bridge rectifier is commonly connected to an input AC voltage for converting the input AC voltage into a full-wave rectified DC voltage before the voltage is stepped-up. However, the rectifying diodes that constitute the bridge rectifier cause considerable conduction loss resulting in power conversion efficiency degradation. As such, conventional PFC boost converters that include a bridge rectifier typically fail to provide sufficient efficiency for high power applications.

PFC boost converters that do not include a bridge rectifier, commonly referred to as bridgeless PFC boost converters, provide improved efficiency and reduced conduction loss compared to similar PFC boost converters having a bridge rectifier. FIG. 1 illustrates a circuit diagram of a conventional bridgeless power factor correction boost converter. In FIG. 1, a boost inductor L11 is coupled to a first node on an input AC voltage, and a boost inductor L12 is coupled to a second node of the input AC voltage. A transistor switch S11 is coupled to the boost inductor L11, and a transistor switch S12 is coupled to the boost inductor L12. A rectifying diode D11 is coupled to the boost inductor L11 and also in series with the transistor switch S11. A rectifying diode D12 is coupled to the boost inductor L12 and also in series with the transistor switch S12. The rectifying diodes D11, D12 are coupled to an output capacitor C11 through a first bus and the transistor switches S11, S12 are coupled to the output capacitor C11 through a second bus. The output capacitor C11 is coupled to a load R11.

During a positive half-cycle of the input AC voltage, the transistor switch S11 is turned on and an input current is induced to flow toward the boost inductor L11 so as to charge the boost inductor L11. Concurrently with the transistor switch S11 turned on, the transistor switch S12 is also turned on and the current path is closed through the body diode of the transistor switch S12. Next, still during the positive half-cycle of the input AC voltage, the transistor switch S11 is turned off and the energy stored in the boost inductor L11 is discharged to the output capacitor C11 through the rectifying diode D11. The current path is closed through the body diode of the transistor switch S12, where the current path is from the input AC voltage, through the boost inductor L11, through the rectifying diode D11, through the output capacitor C11, through the body diode of the transistor switch S12, through the boost inductor L12 and back to the input AC voltage.

During the negative half-cycle of the input AC voltage, the transistor switch S12 is turned on and an input current is induced to flow toward the boost inductor L12 so as to charge the boost inductor L12. Concurrently with the transistor switch S12 turned on, the transistor switch S11 is also turned on and the current path is closed through the body diode of the transistor switch S11. Next, still during the negative half-cycle of the input AC voltage, the transistor switch S12 is turned off and the energy stored in the boost inductor L12 is discharged to the output capacitor C11 through the rectifying diode D12. The current path is closed through the body diode of the transistor switch S11. As such, during each half-cycle of the input AC voltage, one transistor switch functions as an active switch and the other transistor switch functions as a rectifying diode. A disadvantage of the converter shown in FIG. 1 is that output voltage value floats compared to the input AC voltage and ground. Another disadvantage is that the converter of FIG. 1 suffers from a severe EMI noise problem due in part to the increase of the parasitical capacitance value between the buses and ground.

FIG. 2 illustrates a circuit diagram of another conventional bridgeless power factor correction boost converter. The bridgeless power factor correction boost converter of FIG. 2 is a modified circuit diagram of the bridgeless power factor correction boost converter of FIG. 1. The boost inductors L21, L22, the transistor switches S21, S22, the rectifying diodes D21, D22, and the output capacitor C21 of FIG. 2 are configured and operate similarly to the configuration and operation of the of the boost inductors L11, L12, the transistor switches S11, S12, the rectifying diodes D11, D12, and the output capacitor C11, respectively, of FIG. 1. The bridgeless PFC boost converter of FIG. 2 adds a pair of auxiliary diodes D23, D24 to the input side of the converter to more efficiently suppress the EMI noise of the converter. However, power loss across the diodes D23, D24 lowers the circuit efficiency.

SUMMARY OF THE INVENTION

Embodiments are directed to a bridgeless PFC boost converter having two auxiliary transistor switches coupled to an input AC voltage source. The bridgeless PFC boost converter also includes two boost inductors coupled to opposing ends of an input AC voltage source. A first of the boost inductors is coupled to a junction node of a first rectifying diode and a first transistor switch coupled in series. A second of the boost inductors is coupled to a junction node of a second rectifying diode and a second transistor switch coupled in series. The first and second rectifying diodes are commonly coupled to first node of an output capacitor, and the first and second transistor switches are commonly coupled to a second node of the output capacitor. A first of the auxiliary transistor switches is commonly coupled with the first boost inductor and to a first node of the input AC voltage source. A second of the auxiliary transistor switches is commonly coupled with the second boost inductor and to a second node of the input AC voltage source. In some embodiments, the each of the transistor switches, each of the auxiliary switches and the output capacitor are commonly coupled to ground.

In an aspect, a bridgeless power factor correction boost converter includes a first boost inductor, a first transistor, a first rectifying diode, a second boost inductor, a second transistor, a second rectifying diode, an output capacitor, a third transistor and a fourth transistor. The first boost inductor is coupled to a first node of an AC voltage source. The first transistor switch is coupled to the first boost inductor. The first rectifying diode includes an anode coupled to the first boost inductor and the first transistor switch. The second boost inductor is coupled to a second node of an AC voltage source. The second transistor switch is coupled to the second boost inductor. The second rectifying diode includes an anode coupled to the second boost inductor and the second transistor switch. The output capacitor is coupled in parallel to the first rectifying diode and the first transistor switch and in parallel to the second rectifying diode and the second transistor switch. The third transistor switch is coupled to the first node of the AC voltage source. The fourth transistor switch is coupled in parallel to the second boost inductor and the second transistor switch. In some embodiments, a cathode of the first rectifying diode, a cathode of the second rectifying diode, and a first node of the output capacitor are commonly coupled. In some embodiments, a first node of the fourth transistor switch is coupled to the second node of the AC voltage source. In some embodiments, a first node of the third transistor switch is coupled to the first node of the AC voltage source. In some embodiments, a first node of the first transistor switch is coupled to the anode of the first rectifying diode and a first node of the second transistor switch is coupled to the anode of the second rectifying diode. In some embodiments, a second node of the first transistor switch, a second node of the second transistor switch, a second node of the third transistor switch, a second node of the fourth transistor switch and a second node of the output capacitor are commonly coupled. In some embodiments, a first node of the first boost inductor is coupled to the first node of the AC voltage source and a second node of the first boost inductor is coupled to the anode of the first rectifying diode and the first terminal of the first transistor switch, wherein a first node of the second boost inductor is coupled to the second node of the AC voltage source and a second node of the second boost inductor is coupled to the anode of the second rectifying diode and the first terminal of the second transistor switch. In some embodiments, the first transistor switch, the second transistor switch, the third transistor switch and the fourth transistor switch each include a metal-oxide-semiconductor field effect transistor. In some embodiments, the first transistor switch and the third transistor switch are configured to perform switching functions in synchronization with a cycle of the AC voltage source, and the second transistor switch and the fourth transistor switch are configured to perform switching functions in synchronization with the cycle of the AC voltage source.

BRIEF DESCRIPTION OF THE DRAWINGS

Several example embodiments are described with reference to the drawings, wherein like components are provided with like reference numerals. The example embodiments are intended to illustrate, but not to limit, the invention. The drawings include the following figures:

FIG. 1 illustrates a circuit diagram of a conventional bridgeless power factor correction boost converter.

FIG. 2 illustrates a circuit diagram of another conventional bridgeless power factor correction boost converter.

FIG. 3 illustrates a circuit diagram of a bridgeless power factor correction boost converter according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present application are directed to a bridgeless PFC boost converter. Those of ordinary skill in the art will realize that the following detailed description of the bridgeless PFC boost converter is illustrative only and is not intended to be in any way limiting. Other embodiments of the bridgeless PFC boost converter will readily suggest themselves to such skilled persons having the benefit of this disclosure.

Reference will now be made in detail to implementations of the bridgeless PFC boost converter as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts. In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application and business related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.

Embodiments of the bridgeless PFC boost converter are directed to a circuit and method of operating the circuit that provides improved efficiency, reliability and EMI noise performance compared to conventional bridgeless PFC boost converters. The bridgeless PFC boost converter includes two auxiliary transistor switches coupled to an input AC voltage source.

FIG. 3 illustrates a circuit diagram of a bridgeless power factor correction boost converter according to an embodiment. In FIG. 3, a first node of a boost inductor L31 is coupled to a first node on an input AC voltage source, and a first node of a boost inductor L32 is coupled to a second node of the input AC voltage source. A first node of a transistor switch S31 is coupled to a second node of the boost inductor L31 and to an anode of a rectifying diode D31. A first node of a transistor switch S32 is coupled to a second node of the boost inductor L32 and to an anode of a rectifying diode D32. A cathode of the rectifying diode D31 and a cathode of the rectifying diode D32 are coupled to a first node of an output capacitor C31. A second node of the transistor switch S31 and a second node of the transistor switch S32 are coupled to a second node of the output capacitor C31. The output capacitor C31 is coupled in parallel to a load R31.

The bridgeless PFC boost converter also includes a pair of auxiliary transistor switches S33 and S34. A first node of the auxiliary transistor switch S33 is coupled to the first node of the input AC voltage source and to the first node of the first boost converter L31. A first node of the auxiliary transistor switch S34 is coupled to the second node of the input AC voltage source and to the first node of the boost inductor L32. A second node of the auxiliary transistor switch S33 and a second node of the auxiliary transistor switch S34 are commonly coupled to the second node of the transistor switch S31, the second node of the transistor switch S32 and the second node of the output capacitor C31. In some embodiments, the second nodes of each of the auxiliary transistor switch S33, the auxiliary transistor switch S34, the transistor switch S31, the transistor switch S32 and the output capacitor C31 are coupled to ground. The pair of auxiliary transistor switches S33, S34 further suppress the EMI noise of the converter.

In some embodiments, each of the transistor switches S31, S32 and each of the auxiliary transistor switches S33, S34 are metal-oxide-semiconductor field-effect transistors (MOSFETs). Alternatively, other types of semiconductor transistors can be used.

The bridgeless PFC boost converter of FIG. 3 provides many advantages. The conduction loss of an auxiliary transistor switch, such as a MOSFET, is very low. Using auxiliary transistor switches instead of auxiliary diodes, such as the conventional bridgeless PFC boost converter of FIG. 2, improves overall efficiency by reducing conduction losses. Further, reliability of the circuit is improved because the driving signals used to control the auxiliary transistor switches S33, S34 are similar, if not the same, as the driving signals used to control the transistor switches S31, S32. As such, the control circuitry used to provide the driving signals to each of the transistor switches is simplified. Still further, the output ground is tied to the input AC line through the auxiliary transistor switches S33, S34, thus improving the EMI performance compared with the conventional bridgeless PFC boost converter of FIG. 1. Even still further, current sense and voltage sense are easily detected, and therefore there is no need for detecting zero-voltage or zero-current crossings. This saves component count and reduces cost.

The present application has been described in terms of specific embodiments incorporating details to facilitate the understanding of the principles of construction and operation of the bridgeless PFC boost converter. Many of the components shown and described in the various figures can be interchanged to achieve the results necessary, and this description should be read to encompass such interchange as well. As such, references herein to specific embodiments and details thereof are not intended to limit the scope of the claims appended hereto. It will be apparent to those skilled in the art that modifications can be made to the embodiments chosen for illustration without departing from the spirit and scope of the application. 

What is claimed is:
 1. A bridgeless power factor correction boost converter comprising: a. a first boost inductor coupled to a first node of an AC voltage source; b. a first transistor switch coupled to the first boost inductor; c. a first rectifying diode comprising an anode coupled to the first boost inductor and the first transistor switch; d. a second boost inductor coupled to a second node of an AC voltage source; e. a second transistor switch coupled to the second boost inductor; f. a second rectifying diode comprising an anode coupled to the second boost inductor and the second transistor switch; g. an output capacitor coupled in parallel to the first rectifying diode and the first transistor switch and in parallel to the second rectifying diode and the second transistor switch; h. a third transistor switch coupled to the first node of the AC voltage source; and i. a fourth transistor switch coupled in parallel to the second boost inductor and the second transistor switch.
 2. The bridgeless power factor correction boost converter of claim 1 wherein a cathode of the first rectifying diode, a cathode of the second rectifying diode, and a first node of the output capacitor are commonly coupled.
 3. The bridgeless power factor correction boost converter of claim 2 wherein a first node of the fourth transistor switch is coupled to the second node of the AC voltage source.
 4. The bridgeless power factor correction boost converter of claim 3 wherein a first node of the third transistor switch is coupled to the first node of the AC voltage source.
 5. The bridgeless power factor correction boost converter of claim 4 wherein a first node of the first transistor switch is coupled to the anode of the first rectifying diode and a first node of the second transistor switch is coupled to the anode of the second rectifying diode.
 6. The bridgeless power factor correction boost converter of claim 5 wherein a second node of the first transistor switch, a second node of the second transistor switch, a second node of the third transistor switch, a second node of the fourth transistor switch and a second node of the output capacitor are commonly coupled.
 7. The bridgeless power factor correction boost converter of claim 6 wherein a first node of the first boost inductor is coupled to the first node of the AC voltage source and a second node of the first boost inductor is coupled to the anode of the first rectifying diode and the first terminal of the first transistor switch, further wherein a first node of the second boost inductor is coupled to the second node of the AC voltage source and a second node of the second boost inductor is coupled to the anode of the second rectifying diode and the first terminal of the second transistor switch.
 8. The bridgeless power factor correction boost converter of claim 1 wherein the first transistor switch, the second transistor switch, the third transistor switch and the fourth transistor switch each comprise a metal-oxide-semiconductor field effect transistor.
 9. The bridgeless power factor correction boost converter of claim 1 wherein the first transistor switch and the third transistor switch are configured to perform switching functions in synchronization with a cycle of the AC voltage source, and the second transistor switch and the fourth transistor switch are configured to perform switching functions in synchronization with the cycle of the AC voltage source. 